Vehicle restraints increase the safety of loading and unloading trucks at a loading dock. After backing into a loading dock, the truck driver often cannot see the workers loading and unloading cargo from behind. The workers then, sometimes driving forklifts, become vulnerable to accidental movement of the truck away from the loading dock. Federal regulations require that all trucks have an ICC bar spanning across its back end, below the bed. By locking onto the ICC bar with a hook, the vehicle restraint prevents movement of the truck away from the loading dock.
One type of vehicle restraint is commonly called an "impact-style" restraint, such as that disclosed in U.S. Pat. No. 4,264,259 (the '259 patent). The restraint includes an upwardly biased carriage vertically movable along a track between a highest position, where the carriage is stored, and a lowest position. The restraint also includes a power-driven hook used to restrain (e.g., engage) the ICC bar, and the carriage includes two cammed walls between which the hook lies recessed when it is not in the restraining position.
The vehicle restraint in the '259 patent becomes operative when the ICC bar of a vehicle backing into the loading dock contacts the cammed walls of the carriage, forcing the carriage downward along the tracks. The carriage comes to an equilibrium position once the ICC bar reaches the horizontal top face of the cammed walls. After the ICC bar is in place, the hook is actuated. Upon actuation, the hook emerges from the carriage to restrain the ICC bar.
The upwardly biased carriage in the '259 restraint assists the restraint in remaining engaged with the ICC bar. During a loading or unloading of a vehicle, float caused by movement of forklifts, workers, and cargo can change the vehicle's vertical position relative to the drive surface up to ten inches between its heaviest and lightest loads. The upward bias on the carriage maintains the restraint in contact with the ICC bar so that the hook remains engaged with the ICC bar as the truck bed floats.
A major drawback of the '259 reference, however, lies in the initial contact between the ICC bar and the cammed walls of the vehicle restraint. This contact can potentially burden the vehicle restraint with harmful wear and tear. At the same time, the ICC bar can become damaged through deformation when objects or debris lodged in the tracks impede the downward motion of the carriage. Not only does a damaged ICC bar run the risk of being out of compliance with federal regulations, but also, once the damage becomes significant, even an upwardly biased carriage may not bring the hook within range of the ICC bar.